The paper explores the likely macroeconomic impact of imposing a carbon tax at levels sufficient to reduce CO2 emissions significantly. Many studies have indicated the probability of such a tax entailing substantial economic costs. However, such studies have not tended to take into account the possible positive effects of using carbon tax revenues to reduce distortionary taxes elsewhere in the economy or to offset competitiveness effects, or of the possibility that a carbon tax will stimulate innovation and efficiency in the energy sector, with positive economic results. The paper concludes that when these factors are given due weight imposing a carbon tax is more likely to entail economic benefit than cost.